In presses and dies it has been common to utilize metal coil springs that fit in cylindrical pockets in a die in order to absorb the force of various operations such as metal stamping operations. It has also been common to design tooling such that they incorporate gas cylinders which are either associated with a manifold or self contained. In a manifold type, a plurality of gas cylinders are mounted in a manifold or connected to a line and gas from the manifold or line is maintained on each gas cylinder, as shown, for example, in U.S. Pat. Nos. 4,528,838, 4,529,181, 4,572,489, 4,583,722 4,628,796 and 4,742,997.
Such cylinders are complex and expensive and therefore have been found to be less used in lightweight part manufacture.
When coil springs are utilized in tooling, a large number of such coil springs are required. Furthermore, they tend to fatigue and break in which case the fragments can damage the tooling. Casings have been used about each coil spring to minimize such damage. It has hereto been proposed that a self contained gas spring be interchangeable with a metal coil spring as shown in U.S. Pat. No. 4,741,518.
As set forth in U.S. Pat. No. 4,741,518, a self contained gas spring interchangeable with a coil spring comprises a cylindrical body having a constant diameter external cylindrical surface, the cylindrical body having open ends and a piston within said cylindrical body and having one end projecting through one of the openings of the cylindrical body. The piston and the cylindrical body have interengaging flanges that limit the outward movement of the piston relative to the cylindrical body. A plug is positioned in the other end of the cylindrical body to close the opening of the cylindrical body. A charging valve is positioned in the plug for charging the interior of the gas spring. The piston has a hollow inner end with an inner surface tapering outwardly and axially toward the plug. The plug has a generally complementary surface such that the piston can move downwardly about a portion of the plug thereby substantially reducing the height of the gas spring. Such a gas spring is effective for the intended purpose. However, it is likely to be subjected to contamination by oil or other external contaminants passing downwardly along the piston.
Among the objectives of the present invention are to provide a small gas cylinder which is relatively low in cost and be used either in die systems that are provided in connection with a manifold or valve blocks for supplying gas to a plurality of cylinders or in the form of a self-contained gas cylinder or spring; a small gas spring which is interchangeable with a coil spring; which can be readily substituted for a coil spring without any change in the tooling; which is compact and effective for the intended purpose; which obviates the deleterious effects of oil or other contaminants from the exterior of the press or die; which can be readily assembled; which will be retained in position in case of dissipation or loss of gas pressure without risk of damage to the tooling; which does not require any separate casing as is used in coil springs; and which can be provided in various sizes to produce the desired forces so that the gas spring can replace a plurality of coil springs.
In accordance with the invention, the gas cylinder for use in die systems for forming lightweight parts. In one form, the cylinder forms a self contained gas spring which is interchangeable with a coil spring that is constructed such that it is not adversely affected by the deleterious effects of oil and other contaminants. The gas cylinder comprises a one-piece cylindrical upper body having a base wall and a peripheral wall and a hollow rod extending upwardly into the cylindrical body such that the upper body completely encircles and encloses the upper end of the rod. The rod has a base having an outer diameter greater than the diameter of the rod. The peripheral wall of the cylinder and the outer diameter of the base have substantially the same diameter such that the cylinder can be positioned in a recess of a press or die in place of a coil spring. The cylindrical body and rod include interengaging portions limiting axially outwardly movement of the cylinder relative to the rod. In one form, the cylinder further includes a charging valve in the base of the rod through which gas may be introduced for charging the space between the cylinder and the rod and a pressure relief rupture disk in the base wall of the cylindrical body. In another form, a threaded axial projection is provided on the rod. In another form, the opening in the hollow rod is exposed and the base is formed with an axial projection that is threaded for engagement into a manifold or valve block used in the die system.